698 Integrate spotbugs and fix many potential java bugs

[commjoen]

What kind of changes does this PR include?

• Fixes or refactors
• A new challenge
• Additional documentation
• Something else: implements spotbugs as part of the OSSF passing criteria

Description

Given CodeqL is not FOSS, we have to implement something else that fulfills the scanning criteria. Spotbugs is on their list.

Relations

Closes #698

References

See https://bestpractices.coreinfrastructure.org/en/projects/7024#security:~:text=Static%20code-,analysis,-Met

Checklist:

• All the contributions made are solely the work of me and my co-authors
• I tested the changes in this PR (if applicable)
• I added unit tests to ensure my change works (when change in Java or on front-end code)
• The PR passes pre-commit hooks and automated tests
• All spotbugs findings are fixed
• Spotbugs github workflow
• Patch some of the dependency check findings

[bendehaan]

Looks like this was some work! Nice! 👏